This invention relates generally to driveshaft assemblies for automotive land vehicles and more particularly to dynamically balanced driveshaft assemblies and methods for dynamically balancing such driveshaft assemblies.
Commercially produced driveshaft assemblies for automotive land vehicles generally comprise a thin walled tube having a yoke welded or otherwise suitably attached to each end. Due to manufacturing tolerances, these tubular driveshafts are neither perfectly round in cross section, absolutely straight throughout their length or exactly uniform in wall thickness. Small deviations in roundness, straightness and wall thickness result in dynamic imbalance that can cause excessive bearing loads during operation particularly at high speed.
Steel driveshaft assemblies are customarily dynamically balanced by welding small steel plates at the end or ends of the driveshaft where the thin walled is supported internally by a yoke and/or along the length of the driveshaft. Welding the small plates to the thin walled tubes can cause thermally induced distortions that result in bowing of the driveshaft and more imbalance.
Moreover, there is an increasing use of aluminum and aluminum based driveshafts and driveshaft components which do not weld as easily as steel. For instance, aluminum and aluminum based driveshafts and driveshaft components cannot be resistance welded. Furthermore, aluminum or aluminum based components are not easily welded to steel components. Consequently there is a need for new methods for attaching balancing weights to driveshafts, particularly steel or other heavy metal balancing weights to aluminum or aluminum based driveshafts or driveshaft components.
Recent proposals for attaching balancing weights to driveshafts include non-welding methods.
For instance, U.S. Pat. No. 4,998,448 granted to William P. Ellis, Jr. Mar. 12, 1991 discloses an aluminum driveshaft that is balanced by applying predetermined amounts of a balancing composition at selected locations on the outer surface of the driveshaft. The balancing composition includes a polymer carrier of an adhesive composition that is cured by ultraviolet light and a particulate material of higher density dispersed in the carrier. The material includes metal particles that have a particle size in the range of 0.080 to 0.120 inches and that comprise 90% to 94% of the balancing composition by weight.
U.S. Pat. No. 4,895,551 granted to Peter J. Fritz Jan. 23, 1990 discloses a fiber reinforced resin driveshaft that is dynamically balanced by applying a mass or patch of resin containing high density particles, such as metal particles to one or more locations on the drive shaft. Each patch extends only a portion of the circumference of the shaft and generally has an area less than 10 sq. inches, and generally has a thickness less than {fraction (1/16)}th inch. The small masses or patches of resin may be attached anywhere along the length of the driveshaft.
These two methods of attaching balancing weights to driveshafts eliminate the need for welding and the problems associated with welding aluminum or aluminum based components. However, these methods have their own drawbacks. For instance, the methods require the selection and preparation of a suitable balancing composition that bonds well to aluminum or aluminum based materials. This selection and/or preparation of a suitable balancing composition could be very difficult and in any event would be considerably more difficult and expensive than simply providing steel or other high density metal plates. Moreover the balancing must be dispensed in a precisely metered quantity at a precise location on the driveshaft and then cured. This adds to the complexity and expense of the process.
U.S. Pat. No. 4,887,989 granted to Norman C. Kerecman Dec. 19, 1989 discloses another driveshaft that is dynamically balanced without any need for welding. In this instance, the driveshaft is dynamically balanced by securing small curved metal plates to one or more locations along the length of the tubular driveshaft by blind rivets. The tubular driveshaft and the curved plates have aligned openings that receive the blind rivets from the exterior of the tubular shaft and then have their inner ends upset to provide a mechanical connection between the curved metal plates and the tubular shaft. A layer of adhesive is interposed between each curved metal plate and the tubular shaft to bond and seal the metal plate to the outer surface of the shaft. The metal plates may be attached anywhere along the length of the driveshaft.
This method of attaching balancing plates also eliminates the need for welding and the problems associated with welding. However, the method also has its own drawbacks. Attachment holes must be located and drilled through the wall of the tubular driveshaft at several locations. This tends to weaken the driveshaft. Furthermore the balancing plates must be bonded to the driveshaft so that water or other material cannot leak through the attachment holes and imbalance the driveshaft during service. This adds further complexity and expense.
It is also known that steel or other metal balancing plates can be attached to an aluminum or aluminum based driveshaft by fusion welding the balancing plates to the driveshaft. In this method, the balancing plates are drilled through to provide a well when the balancing plates are held against an exterior surface of the driveshaft. These wells are then filled with molten aluminum or aluminum based metal that welds easily to the driveshaft and forms secure mechanical fasteners for the steel balancing plates when cooled. While this method is successfully employed in many instances, it too has some drawbacks. For instance the wells are filled by consuming weld wire that is expensive. Furthermore, the method has a high scrap rate due to the tendency for the molten metal in the well of the balancing plate to burn through the tubular driveshaft if the process is not controlled very precisely.
The object of this invention is to provide a driveshaft assembly comprising an aluminum, aluminum or other metallic driveshaft that is dynamically balanced easily and economically.
A feature of the invention is that the driveshaft assembly is dynamically balanced without any need for drilling holes in the driveshaft.
Another feature of the invention is that the driveshaft assembly is dynamically balanced without any need for the selection, preparation and/or application of a balancing composition, slurry or paste.
Another feature of the invention is that the driveshaft assembly is dynamically balanced without any need for wells or large masses of molten material.
Still yet another feature of the invention is that the driveshaft assembly is dynamically balanced by simple steel or other high density metal plates that are securely attached to the driveshaft by studs that do not require drilled holes in the driveshaft, sealants, bonding materials nor large masses of molten material.